1. Field of the Invention
The present invention relates to a receiver, a channel state information compressing method, and a computer program.
Priority is claimed on Japanese Patent Application No. 2010-204524, filed Sep. 13, 2010, the contents of which are incorporated herein by reference.
2. Description of the Related Art
For next-generation wireless communication systems, employment of an MIMO (multiple input multiple output) system has been examined. In the MIMO system, a transmitter performs precoding based on channel state information (CSI) which indicates the state of a signal transmission path (i.e., communication channel) for transmission data, thereby improving frequency usage efficiency in comparison with a case which does not perform such precoding (see, for example, Non-Patent Document 1).
In case of FDD (frequency division duplex), channel state information is generally acquired by a receiver. In a known method of precoding transmission data based on the channel state information, the channel state information (e.g., channel response matrix) obtained by the receiver is sent to a transmitter, and the transmitter performs precoding based on the relevant channel state information.
However, when the channel state information obtained by the receiver is directly sent to the transmitter, the amount of transmission data is massive. Therefore, as a method for reducing the amount of data sent from a receiver to a transmitter, Non-Patent Document 2 is known. In the known channel state information compressing technique disclosed in Non-Patent Document 2, channel state information is subjected to DCT (discrete cosine transform), and only data having a relatively high electric power among data after DCT is sent to the transmitter.    Non-Patent Document 1: M. Vu, A. Paulraj, “MIMO Wireless Linear Precoding”, IEEE Signal Processing Magazine, pp. 86-105, September 2007.    Non-Patent Document 2: Y. Hatakawa, S. Konishi, “Performance Evaluation of the Proposed CSI Compression Scheme with Channel Estimation Error and Feedback Delay”, IEICE Technical Report, RCS2009-227, pp. 115-120, January 2010
For the above-described channel state information compressing technique, improvement in the reduction efficiency for the amount of data of the channel state information (sent from the receiver to the transmitter) has been desired. When sending a signal from a transmitter to a receiver via multiple communication channels, there are channel state information items respectively corresponding to the communication channels. For such a case, in order to improve the reduction efficiency for the amount of data of the channel state information, when subjecting the channel state information items to DCT, it is important how to select each information item so as to form DCT input data for collectively performing DCT.